Detection for four pair powered devices

ABSTRACT

A twin power sourcing equipment constituted of: a first power sourcing equipment; and a second power sourcing equipment arranged for connection to a powered device over respective power paths; the first and second power sourcing equipments arranged to: simultaneously perform detection of the powered device; and in the event that at least one of the first and second power sourcing equipments detects the presence of the powered device, alternately perform detection of the powered device to detect a signature impedance; and in the event that each of the alternate detection is indicative of the presence of the signature impedance, provide power to the powered device simultaneously by the first and second power sourcing equipment. Power is not provided to the powered device in the event that the simultaneous detection is indicative of the absence of the powered device on each of the first path and the second path.

BACKGROUND OF THE INVENTION

The invention relates generally to the field of power over local areanetworks, particularly Ethernet based networks, and more particularly toa method of detection and determination of a type of powered deviceattached over four twisted wire pairs.

Power over Ethernet (PoE), in accordance with both IEEE 802.3af-2003 andIEEE 802.3at-2009, each published by the Institute of Electrical andElectronics Engineers, Inc., New York, the entire contents of each ofwhich is incorporated herein by reference, defines delivery of powerover a set of 2 twisted wire pairs without disturbing datacommunication. The aforementioned standards particularly provide for apower sourcing equipment (PSE) and a powered device (PD). The powersourcing equipment is configured to detect the PD by ascertaining avalid signature resistance, and to supply power over the 2 twisted wirepairs only after a valid signature resistance is actually detected.

U.S. Pat. No. 7,492,059 issued Feb. 17, 2009 to Peker et al, the entirecontents of which is incorporated herein by reference is addressed topowering a PD over 4 twisted wire pairs. Such a technique provides forincreased power as compared to either of the above mentioned standards,and is commercially available from Microsemi Corporation of Alisa Viejo,Calif.

The HD BaseT Alliance of Beaverton Oregon has published the HDBaseTSpecification Version 1.1.0 which defines a high power standardutilizing twisted wire pair cabling, such as Category 5e (CAT 5e) orCategory 6 (CAT 6) structured cabling as defined by ANSI/TIA/EIA-568-A.The specification provides for even higher power than the abovementioned IEEE 802.3at-2009 over each set of 2 pairs, with all 4 pairsutilized for powering, and allows for power over structuredcommunication cabling from any of: a type 1 PSE, denoted hereinafter asa low power

PSE, typically meeting the above mentioned IEEE 802.3af standard; a type2 PSE denoted hereinafter as a medium power PSE, typically meeting theabove mentioned IEEE 802.3at standard; a type 3 PSE, denoted hereinafteras a high power PSE, typically meeting the above HDBaseT specification;twin medium power PSEs; and twin high power PSEs.

Detection, in accordance with any of the above standards requires thesupply of at least 2 voltage levels between the range of 2.8 volts and10 volts, with a signature resistance of the PD determined based on acalculation of the actual voltage levels, or current, detected. The useof 2 voltage levels allows for determination of the signature resistanceirrespective of the existence of a diode bridge, typically supplied atthe input to the PD.

Twin medium power PSEs or twin high power PSEs may be paired with anytype of PD, i.e. a PD which is arranged to receive power over only 2sets of twisted wire pairs, or a PD which is arranged to receive powerover 4 sets of twisted wire pairs, without limitation, and thus the twinmedium power PSEs or twin high power PSEs must be designed to properlydetect the PD irrespective of its arrangement. In the event that a PDarranged to receive power over only 2 sets of twisted wire pairs isconnected, simultaneous detection by each of the twin PSEs wouldinterfere with proper detection, as described in further detail in U.S.Pat. No. 7,492,059, issued Feb. 17, 2009 to Peker et al, and U.S. Pat.No. 7,595,756 issued Sep. 22, 2009 to Ferentz, the entire contents ofboth of which are incorporated herein by reference. Similarly, a PDwhich is supplied without a diode bridge, or in the event that twoseparate PDs are supplied, one on each 2 sets of twisted wire pairs, canonly be properly detected by performing detection on each of the 2 setsof twisted wire pairs.

FIG. 1A illustrates a high level schematic diagram of an alternative A

PoE powering arrangement 10, according to the prior art, comprising: aswitch/hub 20; a plurality of twisted wire pairs 30 constituted within astructured cable 35; and a PD 40. Switch/hub 20 comprises a plurality ofdata transformers 50 and a PSE 60. PD 40 comprises: a plurality of datatransformers 50; a first and a second diode bridge 65; a PD interface70; an electronically controlled switch 80; and a PD load circuitry 90.PD interface 70 comprises: an under-voltage lockout (UVLO) circuit 100;a signature impedance 110; and a class current source 120. Optionally, aclass event counter is further supplied (not shown). PSE 60 comprises adetection functionality 62, a classification functionality 64 and apowering functionality 66, each of which may be constituted in adedicated circuitry, or as a programmed functionality for a computingelement, without limitation. A data pair is connected across the primaryof each data transformer 50 in switch/hub 20 and a first end of eachtwisted wire pair 30 is connected across the secondary of each datatransformer 50 in switch/hub 20 via respective connections, listedconventionally in two groups: connections 1, 2, 3, 6; and connections 4,5, 7 and 8. The outputs of PSE 60 are respectively connected to thecenter taps of the secondary windings of data transformers 50 ofswitch/hub 20 connected to twisted wire pairs 30 via connections 1, 2, 3and 6. Structured cable 35 typically comprises 4 twisted wire pairs 30.

A data pair is connected across the primary of each data transformer 50in PD 40 and a second end of each twisted wire pair 30 is connectedacross the secondary of each data transformer 50 in PD 40 via respectiveconnections, listed conventionally in two groups: connections 1, 2, 3,6; and connections 4, 5, 7 and 8. The inputs of first diode bridge 65are respectively connected to the center taps of the secondary windingsof data transformers 50 of PD 40 connected to twisted wire pairs 30 viaconnections 1, 2, 3 and 6. The inputs of second diode bridge 65 arerespectively connected to the center taps of the secondary windings ofdata transformers 50 of PD 40 connected to twisted wire pairs 30 viaconnections 4, 5, 7 and 8. The positive outputs of first and seconddiode bridges 65 are commonly connected to the positive input of PDinterface 70, and the returns of first and second diode bridges 65 arecommonly connected to the return of PD interface 70. PD interface 70 isillustrated as having a pass through connection from the positive inputto the positive output thereof, and power for each of UVLO circuit 100,signature impedance 110 and class current source 120 are provided therefrom (not shown). PD interface 70 is illustrated as having a passthrough connection from the return input to the return output thereof,and a return for each of UVLO circuit 100, signature impedance 110 andclass current source 120 are provided there from (not shown).Electronically controlled switch 80 is arranged to provide a switchableconnection between the return of PD load circuitry 90 and the return ofPD interface 70, and electronically controlled switch 80 is responsiveto an output of UVLO circuit 100, indicative that received power isreliable and is denoted PG. The positive input of PD load circuitry 90is connected to the positive output of PD interface 70.

Powering arrangement 10 has been illustrated in an embodiment whereinelectronically controlled switch 80 is connected in the return path,however this is not meant to be limiting in any way, and is simply meantas a depiction of one embodiment of alternative A powering known tothose skilled in the art. Similarly, PSE 60 is illustrated as being partof switch/hub 20 however this is not meant to be limiting in any way,and midspan equipment may be utilized to provide a connection for PSE 60without exceeding the scope. PSE 60 may be any equipment arranged toprovide power over communication cabling, including equipment meetingthe definition of a PSE under any of IEEE 802.3af; IEEE 802.3at; and theabove mentioned HDBaseT specification, without limitation.

In operation, electronically controlled switch 80 is initially set toisolate PD load circuitry 90 from PSE 60. PSE 60 detects PD 40 utilizingdetection functionality 62 in cooperation with signature impedance 110presented by PD interface 70. After detection, PSE 60 optionallypresents a classification voltage to PD 40 utilizing classificationfunctionality 64, and class current source 120 is arranged to drive apredetermined current indicative of the power requirements of PD loadcircuitry 90 responsive to the presented classification voltage, thusindicating to PSE 60 the power requirements thereof The amount ofcurrent is detected by classification functionality 64. Optionally, PSE60 further provides PD 40 with information regarding the poweringability of PSE 60 by providing a plurality of classification eventsseparated by mark events, with the information provided by the number ofclassification events. The mark events function to define the individualclassification events. A class event counter, if supplied, is arrangedto count the classification events and output information regarding thecounted classification events to PD load circuitry 90, thus providing PDload circuitry 90 with information regarding the powering ability of PSE60.

PSE 60 is further arranged, in the event that sufficient power isavailable to support the power requirements detected and output byclassification functionality 64, to provide operating power for PD 40over 2 twisted wire pairs 30 of structured cable 35 by raising thevoltage above the classification voltage range responsive to poweringfunctionality 66. First diode bridge 65 is arranged to ensure that powerreceived by PD interface 70 and PD load circuitry 90 is at apredetermined polarity irrespective of the connection polarity of PSE60. UVLO circuit 100 is arranged to maintain isolation between PSE 60and PD load circuitry 90 until a predetermined operating voltage hasbeen achieved across PD interface 70, and upon sensing the predeterminedoperating voltage UVLO circuit 100 is further arranged to assert outputPG thus closing electronically controlled switch 80 thereby providingpower to PD load circuitry 90. Optionally, a timer (not shown) may beprovided to ensure that the startup phase is complete prior to closingelectronically controlled switch 80.

FIG. 1B illustrates a high level schematic diagram of an alternative BPoE powering arrangement 200, according to the prior art, comprising: aswitch/hub 20; a plurality of twisted wire pairs 30 constituted within astructured cable 35; and a PD 40. Alternative B PoE powering arrangement200 is in all respects identical to alternative A PoE poweringarrangement 10 with the exception that the outputs of PSE 60 arerespectively connected to the center taps of the secondary windings ofdata transformers 50 of switch/hub 20 connected to twisted wire pairs 30via connections 4, 5, 7 and 8. The operation of alternative B PoEpowering arrangement 200 is in all respects identical to alternative APoE powering arrangement 10, and in the interest of brevity will not befurther detailed.

FIG. 1C illustrates a high level schematic diagram of a PoE poweringarrangement 300 utilizing twin PSEs to provide power to a PD over 4twisted wire pairs, in accordance with the prior art, comprising: aswitch/hub 20; a plurality of twisted wire pairs 30 constituted within astructured cable 35; and a PD 40. PoE powering arrangement 300 is in allrespects identical to alternative A PoE powering arrangement 10 andalternative B PoE powering arrangement 200 with the exception that afirst and a second PSE 60 are supplied, the outputs of first PSE 60respectively connected to the center taps of the secondary windings ofdata transformers 50 of switch/hub 20 connected to twisted wire pairs 30via connections 1, 2, 3 and 6, representing a first powering path, andthe output of second PSE 60 connected to the center taps of thesecondary windings of data transformers 50 of switch/hub 20 connected totwisted wire pairs 30 via connections 4, 5, 7 and 8, representing asecond powering path. A communication link is provided between the firstPSE 60 and second PSE 60 to provide for the required coordination, aswill be described further. For simplicity, the details of PSE 60 areomitted. The operation of PoE powering arrangement 300 is in allrespects identical to alternative A PoE powering arrangement 10 andalternative B PoE powering arrangement 200 with the exception that poweris supplied by each of first PSE 60 and second PSE 60.

FIG. 1D illustrates the voltage waveform outputs from first PSE 60,denoted waveform 350, and the voltage waveform output from second PSE60, denoted waveform 360, both as experienced at PD interface 70, inaccordance with PoE powering arrangement 300 and in accordance with theprior art, wherein the x-axis represents time and the y-axis representsvoltage in arbitrary units. In order to avoid interference, first PSE 60performs detection of signature impedance 110, and after completion ofthe detection, second PSE 60 performs detection of signature impedance110, with the timing coordinated by the communication link between firstPSE 60 and second PSE 60. After both first PSE 60 and second PSE 60 haveperformed detection, first PSE 60 performs classification in cooperationwith class current source 120, and then second PSE 60 performsclassification in cooperation with class current source 120. Finally,powering is performed, preferably simultaneously, responsive to thecommunication link, by each of first PSE 60 and second PSE 60.

In the event that PD 40, arranged to receive power over all 4 twistedwire pairs, is connected between the detection performed by first PSE 60and detection performed by second PSE 60, as shown by dotted line 370, aproblem occurs. Specifically, first PSE 60 will not provide power on its2 twisted wire pairs, since detection has failed, whereas second PSE 60will provide power on its 2 twisted wire pairs. PD 40, which is arrangedto receive power over all 4 twisted wire pairs, will only receive powerfrom second PSE 60, which may be insufficient for proper operation.Unless PD 40 completely shuts down, detection will not be performedagain by first PSE 60, since power appears on the twisted wire pairsconnected thereto as provided by second PSE 60. Such a condition isproblematic as it leads to unexpected results.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the present invention toovercome the disadvantages of prior art in powering remote devices. Thisis provided in the present invention by a method of detection in whichtwo PSEs associated with a single PD initiate a simultaneous detectionphase prior to performing independent detection. In the event that thesimultaneous detection is indicative that no PD is connected on eitherpath, i.e. both PSEs return a high impedance result, powering of the PDis not performed by either of the PSEs. In one embodiment, alternatedetection is not performed in the event that the simultaneous detectionis indicative that no PD is connected on either path.

Additional features and advantages of the invention will become apparentfrom the following drawings and description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and to show how the same maybe carried into effect, reference will now be made, purely by way ofexample, to the accompanying drawings in which like numerals designatecorresponding sections or elements throughout.

With specific reference now to the drawings in detail, it is stressedthat the particulars shown are by way of example and for purposes ofillustrative discussion of the preferred embodiments of the presentinvention only, and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of the invention. In this regard, noattempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention, the description taken with the drawings making apparent tothose skilled in the art how the several forms of the invention may beembodied in practice. In the accompanying drawings:

FIG. 1A illustrates a high level block diagram of a first alternativePoE powering arrangement known to the prior art;

FIG. 1B illustrates a high level block diagram of a second alternativePoE powering arrangement known to the prior art;

FIG. 1C illustrates a high level block diagram of an alternative PoEpowering arrangement known to the prior art, wherein power is suppliedto a PD from a first and a second PSE;

FIG. 1D illustrates the voltage waveform outputs from the first andsecond PSE of the powering arrangement of FIG. 1C known to the priorart;

FIG. 2 illustrates a high level block diagram of an exemplary twin PSE,each of the constituent PSEs comprising a control circuitry;

FIG. 3 illustrates a high level block diagram of an exemplary networkconfiguration for remote powering from a twin PSE;

FIG. 4 illustrates an exemplary embodiment of the voltage waveformoutputs from the first and second PSE of the twin PSE of FIG. 3; and

FIG. 5 illustrates an exemplary high level flow chart of the operationof the twin PSE of FIG. 3 to detect and provide power to a PD.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is applicable to other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

The invention is being described as an Ethernet based network, with apowered device being connected thereto. It is to be understood that thepowered device is preferably an IEEE 802.3 compliant device preferablyemploying a 10Base-T, 100Base-T or 1000Base-T connection.

FIG. 2 illustrates a high level block diagram of an exemplary twin PSE400 comprising a first PSE 60 and a second PSE 60. Each PSE 60comprises: a control circuitry 410; a detection functionality 62, aclassification functionality 64 and a powering functionality 66, each ofwhich may be constituted in a dedicated circuitry, or as a programmedfunctionality for a computing element, without limitation. Controlcircuitry 410 of each PSE 60 is in communication with each of therespective detection functionality 62, classification functionality 64and powering functionality 66. Control circuitry 410 of a first PSE 60of twin PSE 400 is in communication with a control circuitry 410 of asecond PSE 60 of twin PSE 400. In one embodiment (not shown) a singlemaster control circuitry is supplied for both PSEs 60 of twin PSE 400.In one embodiment, each control circuitry 410 of twin PSE 400 can act asa master control circuitry, or as a slave control circuitry, with theother control circuitry 410 of twin PSE 400 respectively acting as aslave control circuitry or master control circuitry. The operation oftwin PSE 400 will be described further below in relation to FIGS. 3-5.

FIG. 3 illustrates a high level block diagram of an exemplary networkconfiguration 500 for remote powering from a twin PSE 400. Networkconfiguration 500 is in all respects identical with networkconfiguration 300, with the exception that the PSEs 60 are combined intoa single twin PSE 400, and whose operation is in accordance with thedescription below. As described above first PSE 60 is connected over afirst path 510 to provide power to PD 40, first path 510 constituted oftwo twisted wire pairs 30 via connections 1, 2, 3 and 6. Second PSE 60is connected over a second path 520 to provide power to PD 40, secondpath 520 constituted of two twisted wire pairs 30 via connections 4, 5,7 and 8.

FIG. 4 illustrates an exemplary embodiment of the voltage waveformoutputs from the first PSE 60, denoted waveform 550 and second PSE 60 ofthe twin PSE 400, denoted waveform 560, both as experienced at PDinterface 70, in accordance with network configuration 500, wherein thex-axis represents time and the y-axis represents voltage in arbitraryunits. First PSE 60 and second PSE 60 innovatively first performsimultaneous detection 570 on each of first path 510 and second 520,responsive to the respective control circuitry 410 and detectionfunctionality 62, as illustrated on the left side of each of waveforms550 and 560. Responsive to certain conditions, as will be describedfurther below in relation to FIG. 5, alternate detection 580 isperformed by each of first PSE 60 over first path 510 and second PSE 60over second path 520, responsive to the respective control circuitry 410and detection functionality 62. Optionally, and responsive to certainconditions, as will be described further below, classification 590 isperformed by each of first PSE 60 over first path 510 and second PSE 60over second path 520, alternately, responsive to the respective controlcircuitry 410 and classification functionality 64. Finally, responsiveto certain conditions, as will be described further below, powering ofPD 40 is performed, as shown at 600, preferably simultaneously, by eachof first PSE 60 over first path 510 and second PSE 60 over second path520, alternately, responsive to the respective control circuitry 410 andpowering functionality 66.

The above is illustrated in an embodiment wherein classification is notperformed after simultaneous detection 570, however this is not meant tobe limiting in any way. In other embodiments each of first PSE 60 andsecond PSE 60 perform classification after simultaneous detection 570prior to performing alternate detection 580. In one embodiment theresults of the classification performed after simultaneous detection arediscarded.

FIG. 5 illustrates an exemplary high level flow chart of the operationof the twin PSE 400 to detect and provide power to PD 40. In stage 1000,simultaneous detection of PD 40 is performed by each of first PSE 60over first path 510 and second PSE 60 over second path 520. It is to beunderstood that simultaneous detection may be performed as described inany of the above mentioned standards, thus requiring a plurality ofdetection voltages at a plurality of time intervals, or may be performedas described in U.S. Pat. No. 7,849,343 issued Dec. 7, 2010 to Darshan,et al, the entire contents of which is incorporated herein by reference,thus requiring a single detection voltage, without limitation. Thedetection voltage of U.S. Pat. No. 7,849,343 may be lower than thedetection voltage defined in the above mentioned standards, however forthe purposes of this document, any voltage lower than the maximumallowed detection voltage according the above mentioned standards, andthus does not trigger a classification current source, is considered adetection voltage.

In stage 1010, the results of the simultaneous detection of stage 1000are examined. In the event that the results of the simultaneousdetection are indicative that both powering path 510 and powering path520 are open, i.e. PD 40 is not detected, stage 1000 is again performed.Preferably, stage 1000 is performed only periodically, and thus apredetermined time period is delayed between subsequent simultaneousdetections of stage 1000. The definition of an open powering path is onethat exhibits an impedance well in excess of a valid PD. In oneparticular embodiment, and impedance detected in excess of 100K isdetermined to be an open powering path.

In the event that in stage 1010 the results of the simultaneousdetection are not indicative that both powering path 510 and poweringpath 520 are open, in stage 1020, the actual results of the simultaneousdetection of stage 1000 are stored, preferably in a local memory ofcontrol circuitry 410. In an exemplary embodiment, the results of thesimultaneous detection are categorized as one of: open; fail and pass.The term pass is meant to be synonymous with a valid detection of PD 40,i.e. the detection of a valid signature impedance 110, in accordancewith the relevant specification, or pre-determined values. The term failis meant to include the detection of any value which is not a validsignature impedance 110, and is not defined as an open condition asdescribed above.

Optionally, as described above, classification is performed over each ofpowering path 510, 520 following the simultaneous detection of stage1000. In one embodiment, the results of the classification arediscarded.

In stage 1030, first PSE 60 and second PSE 60 perform alternatedetection on the respective power path 510, 520. The term alternate asused herein is synonymous with the term staggered, in that the detectionare performed such that the waveforms do not overlap with time.Performing the detection alternately prevents interference betweendetection functionalities 62 of first PSE 60 and second PSE 60.

In one embodiment, the stored results of stage 1020 are utilized todetermine which control circuitry 410 acts as a master controlcircuitry, and which control circuitry 410 thus acts as a slave controlcircuitry. In such an embodiment, the control circuitry 410 whoseassociated detection functionality 62 returns a pass value sets itselfas the master, and instructs the other control circuitry 410 to act as aslave. In the event that both detection functionalities 62 return a passvalue, a predetermined one of the two control circuitries 410 assertsitself as master. In one embodiment, the master controls the timing ofboth the PSE 60 of which it is part, and the timing of the PSE 60 of theslave control circuitry 410.

In optional stage 1040, control circuitry 410 of any PSE 60 returning apass value during the alternate detection performs classificationutilizing the respective classification functionality 64. It is to beunderstood that the term pass, is not restricted to the definition inthe above mentioned standards, and other definitions, such as thedetection of a predetermined capacitance as signature impedance 110 maybe utilized without exceeding the scope.

In stage 1050, all paths for which detection functionality 62 hasreturned a pass value during the alternate detection of stage 1030 arepowered. Preferably, powering of a plurality of paths 510, 520 isperformed simultaneously. The term simultaneous is not meant to beexact, and may include a delay between powering small enough to preventdamage to either PSE 60. In one embodiment, the term simultaneous meanswithin 100 microseconds.

The above flow can be modified to detect various non-standardimplementations. Thus, for example certain embodiments present a validsignature impedance to the simultaneous detection of stage 1000, thusresulting in a pass value for each of first PSE 60 and second PSE 60,while presenting ½ of a valid signature impedance to each of thealternate detections of stage 1030. The values of the simultaneousdetection are stored in stage 1020, and thus the raw result of thealternate detection of stage 1030 may be modified to take this resultinto account. In particular, in such an embodiment, a result in stage1000 of pass, for each PSE 60, and a result of fail for each PSE 60 instage 1030 results in reclassification of the fail values to pass, andthus the simultaneous powering of both paths 510, 520.

The above has been described in an embodiment wherein in the event thatstage 1000 presents an open condition for both paths 510 and 520,alternate detection of stage 1030 is not performed, however this is notmeant to be limiting in any way. In an alternative embodiment, an opencondition for both paths 510 and 520 is utilized as a gating conditionfor the powering of stage 1050, without limitation. In such anembodiment, the powering of stage 1050 does not occur in the event thatstage 1000 presents an open condition for both paths 510 and 520.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination. In particular, the invention has beendescribed with an identification of each powered device by a class,however this is not meant to be limiting in any way. In an alternativeembodiment, all powered device are treated equally, and thus theidentification of class with its associated power requirements is notrequired.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meanings as are commonly understood by one of ordinaryskill in the art to which this invention belongs. Although methodssimilar or equivalent to those described herein can be used in thepractice or testing of the present invention, suitable methods aredescribed herein.

All publications, patent applications, patents, and other referencesmentioned herein are incorporated by reference in their entirety. Incase of conflict, the patent specification, including definitions, willprevail. In addition, the materials, methods, and examples areillustrative only and not intended to be limiting.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the present invention isdefined by the appended claims and includes both combinations andsubcombinations of the various features described hereinabove as well asvariations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description.

1. A local area network adapted to supply power to a plurality of types of powered devices over communication cabling, the local area network comprising: a powered device; a first power sourcing equipment; a second power sourcing equipment; and a communication cabling comprising a plurality of twisted wire pairs arranged to connect said first and second power sourcing equipment to said powered device, said communication cabling providing a first power path comprising a first set of twisted wire pairs of said communication cabling between said first power sourcing equipment and said powered device and a second power path comprising a second set of twisted wire pairs of said communication cabling between said second power sourcing equipment and said powered device, said first set different from said second set, said first and second power sourcing equipments arranged to: simultaneously perform detection of the powered device by each applying a detection voltage to said powered device via the respective one of the first path and the second path to detect said powered device, and determine if said powered device is present or absent; and in the event that at least one of said first and second power sourcing equipments detects the presence of the powered device by said simultaneous detection, alternately perform detection of the powered device by each alternately applying the detection voltage to said powered device via the respective one of the first path and the second path to detect a signature impedance; and in the event that each of said alternate detection is indicative of the presence of the signature impedance, provide power to said powered device simultaneously by said first and second power sourcing equipment, wherein the power is not provided to said powered device from either the first power sourcing equipment or the second power sourcing equipment in the event that said simultaneous detection is indicative of the absence of the powered device on each of the first path and the second path.
 2. The local area network of claim 1, wherein in the event that said simultaneous detection is indicative of the absence of the powered device on each of the first path and the second path, said first and second power sourcing equipments do not alternately perform the detection.
 3. The local area network of claim 1, wherein each of said first and second power sourcing equipments are further arranged to perform classification on the respective one of the first and second paths responsive to successful detection of the signature impedance on the respective path by the respective one of the first and second power sourcing equipments, the classification classifying the power requirements of the powered device.
 4. The local area network of claim 3, wherein in the event that only one of said alternate detection is indicative of the presence of the signature impedance, power is provided to said powered device by the respective one of said first and second power sourcing equipment associated with the detection of the presence of the signature impedance, the power provided subsequent to the performed classification.
 5. The local area network of claim 1, wherein in the event that only one of said alternate detection is indicative of the presence of the signature impedance, power is provided to said powered device by the respective one of said first and second power sourcing equipment associated with the detection of the presence of the signature impedance.
 6. The local area network of claim 1, wherein in the event that said simultaneous detection is indicative of the absence of the powered device on each of the first path and the second path, said simultaneously performed detection is repeated after a predetermined time interval.
 7. A twin power sourcing equipment comprising: a first power sourcing equipment arranged for connection to a powered device over a first power path; a second power sourcing equipment arranged for connection to the powered device over a second power path, said second power path different from said first power path; said first and second power sourcing equipments arranged to: simultaneously perform detection of the powered device by each applying a detection voltage to the powered device via the respective one of the first path and the second path to detect the powered device, and determine if the powered device is present or absent; and in the event that at least one of said first and second power sourcing equipments detects the presence of the powered device by said simultaneous detection, alternately perform detection of the powered device by each alternately applying the detection voltage to the powered device via the respective one of the first path and the second path to detect a signature impedance; and in the event that each of said alternate detection is indicative of the presence of the signature impedance, provide power to the powered device simultaneously by said first and second power sourcing equipment, wherein the power is not provided to the powered device from either the first power sourcing equipment or the second power sourcing equipment in the event that said simultaneous detection is indicative of the absence of the powered device on each of the first path and the second path.
 8. The twin power sourcing equipment of claim 7, wherein in the event that said simultaneous detection is indicative of the absence of the powered device on each of the first path and the second path, said first and second power sourcing equipments do not alternately perform the detection.
 9. The twin power sourcing equipment of claim 7, wherein each of said first and second power sourcing equipments are further arranged to perform classification on the respective one of the first and second paths responsive to successful detection of the signature impedance on the respective path by the respective one of the first and second power sourcing equipments, the classification classifying the power requirements of the powered device.
 10. The twin power sourcing equipment of claim 9, wherein in the event that only one of said alternate detection is indicative of the presence of the signature impedance, power is provided to the powered device by the respective one of said first and second power sourcing equipment associated with the detection of the presence of the signature impedance, the power provided subsequent to the performed classification.
 11. The twin power sourcing equipment of claim 7, wherein in the event that only one of said alternate detection is indicative of the presence of the signature impedance, power is provided to the powered device by the respective one of said first and second power sourcing equipment associated with the detection of the presence of the signature impedance.
 12. The twin power sourcing equipment of claim 7, wherein in the event that said simultaneous detection is indicative of the absence of the powered device on each of the first path and the second path, said simultaneously performed detection is repeated after a predetermined time interval.
 13. A method of providing power from a first power sourcing equipment arranged for connection to a powered device over a first power path and a second power sourcing equipment arranged for connection to the powered device over a second power path, the second power path different from said first power path, the method comprising: simultaneously determining, for each of the first power sourcing equipment and the second power sourcing equipment, if the powered device is present or absent; in the event the powered device is determined to be present by both the first power sourcing equipment and the second power sourcing equipment, alternately performing detection of the powered device via the respective one of the first path and the second path to detect a signature impedance; and in the event that each of said alternate detection is indicative of the presence of the signature impedance, providing power to said powered device simultaneously by said first and second power sourcing equipment, wherein said power is not provided to said powered device from either the first power sourcing equipment or the second power sourcing equipment in the event that the powered device is determined to be absent by each of the first power sourcing equipment and the second power sourcing equipment during said simultaneous determining.
 14. The method of claim 13, wherein said simultaneously determining comprises: simultaneously performing detection of the powered device by each applying a detection voltage to said powered device via the respective one of the first path and the second path to detect said powered device, the powered device determined to be present in the event that at least one of said first and second power sourcing equipments detects the presence of the powered device by said simultaneous detection and the powered device determined to be absent in the event that both said first and second power sourcing equipments detect the absence of the powered device by said simultaneous detection, and wherein said alternately performing detection comprises alternately applying the detection voltage to said powered device via the respective one of the first path and the second path to detect a signature impedance.
 15. The method of claim 13, wherein in the event that the powered device is determined to be absent, said alternate detection is not performed.
 16. The method of claim 13, further comprising: performing classification on the respective one of the first and second paths by each of said first and second power sourcing equipments responsive to successful detection of the signature impedance on the respective path by the respective one of the first and second power sourcing equipments, the classification classifying the power requirements of the powered device.
 17. The method of claim 16, further comprising: in the event that only one of said alternate detection is indicative of the presence of the signature impedance, providing power to said powered device by the respective one of said first and second power sourcing equipment associated with the detection of the presence of the signature impedance, the power provided subsequent to the performed classification.
 18. The method of claim 13, further comprising: in the event that only one of said alternate detection is indicative of the presence of the signature impedance, providing power to said powered device by the respective one of said first and second power sourcing equipment associated with the detection of the presence of the signature impedance.
 19. The method of claim 13, wherein in the event that the powered device is determined to be absent by each of the first power sourcing equipment and the second power sourcing equipment during said simultaneous determining, said determining is repeated after a predetermined time interval. 